Commonly known as "identical twins" monozygotic twins are from a single egg that has divided after fertilization to create two embryos. Monozygotic twins consequently share exactly the same genetic material and are of the same sex. Monozygotic twins who have been separated in earliest infancy and raised apart have provided a classic research situation for social scientists. Monozygotic twins, because their genetic identity, yet different social experience, makes it possible to disentangle the separate effects of heredity and social environment. Research on monozygotic twins is essential because the ban on human cloning in many countries worldwide is founded on an assumption that cloned children will be identical to each other and to their nuclear donor.
How identical would cloned children be? An understanding essential to the ethical debate - RG Edwards and HK Beard, Human Reproduction Journals - This paper explores the scientific basis for this assumption, considering both the principles and practice of cloning in animals and comparing genetic and epigenetic variation in potential human clones with that in monozygotic twins.
Cognitive and Personality
Differences Between Identical Twins Following Skull Fractures - Michael J.
Lyons and Adam P. Matheny, The University of North Carolina at Charlotte, University of
Louisville School of Medicine, Journal of Pediatric Psychology 9(4) pp. 485-494, 1984.
The classical co-twin control method was used to evaluate the effects of age at the time of skull fracture on behavioral functioning several years later. The sample consisted of 13 pairs of male monozygotic twins.
Female Monozygotic Twins
with Selective Mutism - A Case Report.
Journal of Developmental & Behavioral Pediatrics. 27(2):129-133, April 2006. - SHARKEY, L; MC NICHOLAS, F.
This case report describes a case of young female monozygotic twins who presented with selective mutism and their treatment spanning a 2-year period. It highlights the strong genetic association along with environmental factors such as social isolation and consequences of maternal social phobia, all contributing to treatment resistance, despite an intensive multimodal biopsychosocial approach. General issues related to the difficulties in treating monozygotic twins are also addressed.
Monozygotic twins discordant for major depression: a preliminary exploration of the role of environmental experiences in the aetiology and course of illness. - KENNETH S. KENDLER and CHARLES O. GARDNER
Background. Genetic effects upon behaviour are pervasive. To what extent are the many correlates of major depression (MD) due to individual-specific environmental experiences versus genetic factors correlated with risk for MD?
Methods. From a population-based twin registry, we identified 72 female monozygotic twin pairs discordant for a lifetime history of MD and compared the affected and unaffected members on a wide range of putative correlates of MD.
Environmental factors cause pervasive differences in monozygotic twins discordant for MD, especially in the areas of interpersonal difficulties, psychopathology, social problems and self-concept.